1. Field of Invention
The invention relates to an antenna and a control system thereof and, more particularly, to a differential antenna and a control system applied to a digital television (TV).
2. Related Art
FIG. 1A is a schematic diagram showing a conventional digital TV receiver applied to a host. Generally, when a user watches a digital TV by using a host 100, he or she needs to connect a digital TV receiver 120 via a connector (such as a universal serial bus connector (USB) of the host 100, and application programs of the digital TV is installed in the host 100. The digital TV receiver 120 includes an antenna 125 and a control unit 128. The antenna 125 is used for receiving a broadcasting signal of the digital TV, and the control unit 128 further converts the broadcasting signal to a selected channel signal. The selected channel signal is the channel selected by the user and transmitted to the host 100.
FIG. 1B is a block diagram showing a conventional digital TV receiver. The control unit 128 of the digital TV receiver 120 includes a low noise amplifier (LNA) 150, a band-pass filter (BPF) 160 and a digital video broadcast (DVB) module 170. The DVB module 170 further includes a radio frequency (RF) tuner 172 and a demodulator 174.
First, after the LNA 150 amplifies the RF signal, the BPF 160 keeps the digital TV bandwidth (about 450 MHz to 870 MHz) of the RF signal and transmits it to the DVB module 170. Second, the DVB module 170 retrieves the selected channel according to the user's instruction and outputs the selected channel signal to the host 100, and the host 100 shows the content of the channel on the screen. The RF tuner 172 processes the bandwidth of the selected channel to a base band signal according to the user's instruction, and the demodulator 174 demodulates the base band signal and converts it to the selected channel signal.
It is well-known that the digital TV system includes the DVB-T system in Europe, the advanced television system committee (ATSC) system in America, the integrated service digital broadcasting (ISDB-T) system in Japan and south America, the digital media broadcasting (DMB-T/H) system in China and so on. The digital TV bandwidth of the systems above is approximately between 460 MHz to 870 MHz. The bandwidth of the DVB-S satellite digital TV system is approximately between 950 MHz to 2150 MHz, and the bandwidth of the ISDB-S satellite digital TV system is approximately between 11.7 GHz to 12.2 GHz.
The length of the antenna is in inverse proportion to a receiving frequency, since the size of the antenna applied to the digital TV in market is large, the antenna cannot be disposed inside the host 100 which is relatively small.
Further, the electromagnetic interference (EMI) occurs in the host 100 in a conventional use, therefore, if the conventional antenna of the digital TV is disposed inside the host 100, the bad receiving signal due to EMI impact would lead to malfunction of the digital TV and cannot be watched.